Yarrowia lipolytica is a non-conventional yeast which has been awarded the Generally Regarded As Safe (GRAS) status by the American Food and Drug Administration (FDA). The GRAS rating of Y. lipolytica makes it suited for the production of bioactive proteins and polypeptides for human applications (Madzak et al., 2004).
Like most other eukaryotes, Yarrowia lipolytica harbors a GPI anchoring machinery and uses it to attach proteins to membranes. Although a few GPI proteins reside permanently at the plasma membrane, a majority of them are further processed and are integrated into the cell wall by a covalent attachment to cell wall glucans.
The GPI biosynthetic pathway is necessary for growth and survival of yeast cells. The GPI lipids are synthesized in the endoplasmic reticulum and added onto proteins by a pathway comprising 12 steps, carried out by 23 gene products, 19 of which are essential. It is estimated that some 60 GPI proteins are predicted from their genomic sequences to serve enzymatic functions required for the biosynthesis and the continuous shape adaptations of the cell wall, others appear to form structural elements of the cell wall and yet others mediate cell adhesion (Benachour et al., 1999).
The prior art teaches that there is no single factor that will improve the production of all heterologous proteins. As a result, there is a need in the art for identifying improved large-scale expression systems capable of secreting extracellular recombinant polypeptides.